Polyamide yarns are commonly produced by melt spinning of one or of a plurality of filaments which are wound onto a container, stored for some time, sometimes referred to as lagging time, and subsequently in a second step drawn and textured. This two-step process produces a yarn with a high crystallinity and a low shrinkage. In addition, a high percentage of the crystals in the two-step yarn are the alpha-type which are more stable than the gamma-type crystals.
One step processes, often referred to as spin-draw-texture (SDT) processes, have been developed which are more efficient but which produce yarns with lower crystallinity and higher shrinkage during the heatsetting process. In addition, these yarns contain a lower percentage of the stable alpha crystals than two-step yarns. The disadvantages of these yarns are the differing deniers of comparable heatset products.
Another disadvantage is the very smooth surface of these yarns which leads to high yarn-to-guide friction in processing the yarns into fabrics which show undesirable non-uniformities such as streaks.
To overcome this latter problem, U.S. Pat. No. 3,414,646 describes a process for the production of polycarbonamide filaments using a treatment of the filaments with steam before the drawing step.
U.S. Pat. No. 3,761,556 discloses a process for the manufacture of a crimped polyamide yarn including a two-stage steaming process prior to drawing and crimping.
In order to improve ozone fading resistance of dyed nylon yarn, U.S. Pat. No. 4,396,570 describes a continuous process for spinning and drawing nylon 6 filaments by applying steam in a chamber to the filaments before the drawing step.
An object of the present invention was to provide a continuous process for spinning and drawing polyamide for the manufacture of polyamide yarns with a high crystallinity, a higher percentage of alpha crystals, and a low shrinkage. Another object was to provide an apparatus for such a process.